Sunak says the government would force parliament to sit late into the night on Monday to pass new legislation if needed.

Sunak said the government had booked commercial charter planes and trained staff to take asylum seekers to Rwanda, a policy he hopes will boost his Conservative Party’s flagging fortunes before an election later this year.

After weeks of opposition in the House of Lords, which wants to introduce safeguards to the divisive legislation, Sunak said the government would force parliament to sit late into the night on Monday if necessary to get it passed.

“No ifs, no buts. These flights are going to Rwanda,” Sunak told a news conference.

Tens of thousands of asylum seekers – many fleeing wars and poverty in Africa, the Middle East and Asia – have reached Britain in recent years by crossing the English Channel in small boats on risky journeys organised by people-smuggling gangs.

The government plans to deport to Rwanda some of those who enter the United Kingdom irregularly as a deterrent to asylum seekers considering making the crossing.

Charities and rights groups say they would try to stop individual deportations and the trade union that represents border force staff is promising to argue the new legislation is unlawful “within days” of the first asylum seekers being informed they will be sent to Rwanda.

Care4Calais, a charity that supports asylum seekers, called the plan an unworkable and cruel “gimmick”.

“We urgently need the UK government to start treating refugees with decency and stop trying to send them away to an unsafe future in Rwanda,” Lucy Gregg, acting head of advocacy at Freedom from Torture, said in a statement.

“Along with survivors of torture and the support of thousands of caring people up and down the country, we will unite to show airlines that we won’t tolerate them flying in the face of human decency.”

The new legislation is Sunak’s answer to a UK Supreme Court ruling last year that sending migrants to Rwanda was illegal under international law.

“Enough is enough. No more prevarication. No more delay,” Sunak told reporters, adding that he envisaged “multiple” flights a month over the summer months.

Stopping the arrivals is a key goal for the government, but critics say the plan to deport people to Rwanda is inhumane and that the East African country is not a safe place.

Some Labour and cross-party peers want the legislation to include safeguards for Afghans who previously helped British troops and to set up a committee to monitor asylum seekers’ safety in Rwanda.

Other European countries, including Austria and Germany, are also looking at agreements to process asylum seekers abroad.